avoid random array items in bash

I have the following code:

n=1

a_letters=("a" "b" "c" "d" "e")

while [ $n -le 3 ]; do
    uniqueLetters=($(printf '%s\n' "${a_letters[@]}"))
    rand=$[ ( $RANDOM % 5)] 
    echo "${uniqueLetters[$rand]}"
    n=$(( $n+1 ))
done

How can I avoid array items that was already printed?